There are known microscope systems with which a plurality of images are captured while moving the viewing field by using an electrically-powered stage or the like and, by pasting (or joining) these images together, large-field, high-resolution microscope images (namely, virtual-slide images, which will hereinafter also be referred to as VS images) are created, and with which the created images are utilized for pathological diagnosis or the like (for example, see Patent Literatures 1 to 3).
When acquiring specimen images by using microscopes, brightness unevenness (shading) occurs in the acquired images due to uneven illumination, nonuniformity of optical systems, unevenness in the sensitivity of image-acquisition devices, and the states of the specimen (surface shape, surface characteristics, thickness, or the like). In virtual microscope systems, with VS images created by pasting together a plurality of images, for example, unnatural changes, such as vertical stripes, horizontal stripes, or the like, appear in the images, which are conspicuous mainly at image-joining portions.
As methods of solving the problem of shading, there are known methods in which shading-correction data are obtained from microscope images of a calibration sample, and in which shading in acquired images of a specimen, which is an observation subject and a measurement subject, is corrected by using the shading-correction data (for example, see Patent Literatures 4 to 6).
In Patent Literature 4, shading correction is performed during transmission-illumination observation by acquiring calibration image data by using a background acquired without a specimen and, during epi-illumination observation, by acquiring calibration image data by using a reflection-only part provided in the microscope system. In Patent Literature 5, shading correction is performed by acquiring calibration image data by using a uniform fluorescent specimen as a calibration specimen. In addition, Patent Literature 6 discloses a method in which shading-correction data are obtained based on changes in brightness of images of a predetermined position between when that position is acquired at the center of the viewing field and when that position is acquired at an edge of the viewing field by using a specimen itself, which is an observation subject and a measurement subject, instead of using a calibration sample.